Interaction between protective antibodies and malaria parasites (Plasmodium berghei): involvement of low avidity antibodies.

Free Plasmodium parasites were incubated with a standardized amount of immune serum in a small volume of fluid or a larger one. When these parasites were tested for infectivity in and in vivo test system the parasites incubated in the larger volume of fluid were more infective. Other aliquots of free P. berghei parasites were incubated with a standaridzed amount of immune serum and then reincubated with or without dilution of the suspending fluid. Those parasites reincubated after dilution were more infective than reincubated without dilution. These results were interpreted as indicating that the malaria parasite-protective antibody interaction is readily reversible probably due to the low avidity of the protective antibodies.